There is a known helmet having a function for ventilating the interior of the helmet, which has a ventilation duct provided on an outer surface of a shell constituting the outermost layer of the helmet, so as to cover ventilating holes provided to pass through between the inner surface of the helmet and the outer surface, and so as to guide air circulated through the ventilating holes.
The ventilation duct disclosed in Patent Document 1 indicated below is provided with two left and right rear duct parts which are arranged on the rear side of the shell, and a front duct part which is arranged so as to connect the rear duct parts with the front side of the shell, and the rear duct parts and the front duct part are integrally formed.